Protocol M98-863 is a Phase III, randomized, double-blind, multi-center, multi-country study of at least 48 weeks duration comparing the administration of ABT-378/Ritonavir plus Stavudine and Lamivudine vs. Nelfinavir plus Stavudine and Lamivudine in antiretroviral-naive HIV-infected subjects. Approximately 660 subjects will be randomized in this study. Subjects will be equally randomized to one of two blinded treatment arms. Approximately 330 subjects will receive 400mg ABT-378/100mg Ritonavir BID plus Nelfinavir placebo TIP, and approximately 330 subjects will receive Nelfinavir 750mg TIP plus ABT-378/Ritonavir placebo BID. All subjects will receive open-label stavudine 30 or 40mg BID (based on weight) and lamivudine 150mg BID in combination with their assigned regimens. Antiretroviral-naive HIV-infected subjects who meet selection criteria will be enrolled. Measurements of vital signs, physical examinations, ECGs, routine clinical laboratory evaluations and determinations of antiviral and immunologic will be performed at intervals.